Developing systems

ABSTRACT

A development system is provided wherein a movable developer loaded applicator surface is first doctored on the edges and corners of the surface to remove excess developer and prevent the accumulation of developer on the corners and is finally doctored with another doctoring surface along the entire applicator surface to provide a uniform distribution of developer on the surface which doctored applicator surface is brought into developing engagement with an image to be developed. Dry and liquid development techniques can be employed and the doctoring surfaces may be provided by doctor blades or rollers.

United States Patent Smith 1 June 6, 1972 54] DEVELOPING SYSTEMS OTHER PUBLICATIONS [72] Inventor: Richard E. Smith, Webster, NY. Wohlaflm, Discrete Stripe Coatings of Magnetic Material," Assigneez xem-X Corporation Rochester, NY Vol. 8 No. 10 March 1966,1BM Tech. Disclosure Bulletin.

22 Filed; t Ju|y 1 9 9 Primary Examiner-Morris Kaplan [52] US. Cl ..l18/637, 117/37 LE, l18/DlG. 23, 355/ 10 [51] Int. Cl. ..G03g 13/00 [58] Field of Search ..1 18/637, 637 LX, 204, 261; 117/37 LX,111R

[56] References Cited UNITED STATES PATENTS 2,397,853 4/1946 Gist ..1 18/261 3,176,611 4/1965 Tripp 118/261 3,176,649 4/1965 Heiseler 118/261 2,604,199 7/l952 Govan ..1 18/261 3,383,209 5/1968 Cassiers et al. ..l17/37 LX Appl. o.5 838,141

Assistant Examiner-Leo Millstein Attorney-James .l. Ralabate, Samuel E. Mott and Albert A. Mahassel [57] ABSTRACT A development system is provided wherein a movable developer loaded applicator surface is first doctored on the edges and corners of the surface to remove excess developer 5 Claims, 6 Drawing Figures PATENTEDJUH 6l972 3.667.428

sum 10F 2 INVENTOR. RICHARD E. SMITH ATTORNEY PATENTEDJUH 6l972 3,667,428

SHEET 2 OF 2 DEVELOPING SYSTEMS BACKGROUND OF THE INVENTION referred to in the art as toner." The toner will normally be attracted to those areas of the layer which retain a charge,

thereby forming a toner image corresponding to the electrostatic latent image. This powder image may then be transferred to a support surface such as paper. The transferred image may subsequently be permanently affixed to a support surface as by heat. instead of latent image formation by uniformly charging the photoconductive layer and then exposing the layer to a light-and-shadow image, one may form the latent image by'directly charging the layer in image configuration. The powder image may be fixed to a photoconductive layer if elimination of the powder image transfer step is desired. Other suitable means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing steps.

Several methods are known for applying a developer to an electrostatic latent image to be developed. One development method as disclosed by E. N. Wise in U. S. Pat. No. 2,618,552, is known as cascade development. Another method of developing electrostatic images is the "magnetic brush" process as disclosed for examplein U. S. Pat. No. 2,874,063. Still another development technique is the powder cloud" process as disclosed by C. F. Carlson in U. S. Pat. No. 2,221,776.

An additional dry development system and the dry system to which this invention is directed involves developing an electrostatic latent image with a powdered developer material, the powder having been uniformly'applied to the surface of a powder applicator! The latent image is brought close enough to the developer powder applicator so that the developer powder is pulledfrom the powder applicator to the charge bearing image in image configuration. The latent image and powder: applicator may desirably be brought in contact including contact 'under pressure to affect development. The powder applicator may be either smooth surfaced or patterned so that the developer powder is carried" in the depressed portions of the patterned surface; Exemplary of this system are the techniques disclosed by H. G. Greig in U. S. Pat. No. 2,811,465.

Liquid developers may also be employed in the developin image configuration.

An additional liquid technique for developing electrostatic latent images is the liquid development process disclosed by R. W. Gundlach in U. S. Pat. No. 3,084,043, hereinafter referred to as Polar Liquid Development. In this method, an electrostatic latent image is developed or made visible by presenting to the imaging surface a liquid developeron the surface of a developer dispensing member having a plurality of raised portions defining a substantially regular patterned sur- 1 face and a plurality of portions depressed below the raised portions. The depressed portions contain a layer of conductive liquid developer which is maintained out of contact with the electrostatographic imaging surface. When the raised areas of the developer applicator are brought into contact with an electrostatic latent image bearing surface, the developer creeps up the sides of the raised areas in contact only with the charged area of the imaging surface, and is deposited thereon.

This technique is to be distinguished from conventional liquid development wherein there is an electrophoretic movement of charged particles suspended in a liquid carrier vehicle to the charged portion of the image bearing surface. That is, the charged particles under the influence of an applied electric field migrate to the charged portion of the image bearing surface while the liquid substantially remains on the applicator surface and serves only as a carrier medium. In polar liquid development the liquid phase actively takes part in the development of the image since the entire liquid developer is attracted to the charged portions of the image bearing surface. Furthermore, in polar liquid development, unlike conventional liquid development, the developer liquid contacts only the charged portions of the image bearing surface.

A further development techniqueis that referred to as wetting development" or selective wetting described in U. S. Pat. No. 3,285,741. In this technique an aqueous developer uniformly contacts the entire imaging surface and due to the selected wetting and electrical properties of the developer substantially only the charged areas of the imaging surface are wetted by the developer. The developer should be relatively conductive having a resistivity generally from about 10 to about 10 ohm-cm and have wetting properties such that the wetting angle measured when placed on the photoconductor surface is smaller than 90 at the charged areas and greater than 90 in the uncharged areas.

-While capable of forming satisfactory images, the electrophoretic development technique, the polar liquid development technique, the selective wetting technique and dry development techniques wherein dry powder is present on a surface to be presented to the latent image to be developed suffer deficiencies in certain areas. In these systems a developer applicator is loaded with developer material to present to the electrostatic latent image to be developed, the necessary quantity of developer for development. In the liquid development techniques, since the developer liquid is loaded onto the applicator surface indiscriminately in excessive quantitles and in a non-uniform configuration, the developer liquid on the surface of the developer applicator must be smoothed out and excess liquid developer removed to present a uniform supply of developer in developing quantities to the image to be developed. This technique is referred to as doctoring and includes both the removal of excess developer liquid while providing a sufficient supply of developer liquid 'on the applicator to present a uniform supply of developer liquid to the electrostatic latent image to be developed. More specifically, in polar liquid development, the developer surface should present a uniform film of developer liquid in the depressed portions or valleys, while the raised portions or lands are sub stantially free of developer. Providingan applicator surface whose lands are substantially free of developer is desired to provide a clean background in non-image areas. These aims are accomplished by providing accurate developer metering techniques and systems and accurate developer doctoring techniques and systems.

The doctoring systems have conventionally taken the form of ablade or squeegee roller. When using a blade doctoring system the blade is positioned on a line along the entire applicator surface so that as this surface is moved, the stationary blade wipes excess ink from the applicator surface. With the appropriate selection of blade material, angle of contact and pressure applied, adequate doctoring may be achieved. The squeegee roller provides a similar doctoring by also being positioned against the applicator surface, and since it may be absorbent it may readily remove excess liquid developer.

, However, regardless'of the specific main doctoring system employed, the edge of the applicator surface and particularly the corner of the applicator surface may contain, excessive quantities of developer which, when in developing configuration, will result in large deposits of developer liquid as background. This may generally be observed as a line or area along the edge of the developed image. This effect is more pronounced when the developing system is used continuously or intermittently over a period of time since some of the excess liquid developer which has accumulated behind the main doctor blade or squeegee roller is forced over the end of the applicator surface and forms a continuous bead on the end surface or comer of the applicator surface. During development, this head of excess developer liquid results in the above mentioned line or area on the developed image. The presence of this excess developer, in addition to appearing as undesired background along the edges of a developed image, is partially transferred to other members of the development apparatus that may be in close proximity and may result in developer liquid contamination of the copy paper or other machine parts. Overall, a rather untidy operation is achieved which produces unclean copies. Furthermore, since this excess liquid developer is wasted, developer liquid consumption is higher than it need be.

Dry development techniques employing conventional toner or other powdered material also manifest these problems to someextent, particularly with respect to the cleanliness and tidiness of operation. In a dry development technique the local accumulationof developer material at the edge and comer of the applicator surface may not be as large as in liquid development operations, and the resulting edge background on the developed image is accordingly smaller. While the local accumulations of dry developer material on the applicator surface are generally not as large as in the liquid development operation, additional fouling and contamination of surfaces and machine members which come in contact with a dry developer material are frequently observed. It is, therefore, clear that there is a continuing need for a better system for developing electrostatic latent images.

SUMMARY OF THE INVENTION It is, therefore, an object of the invention to provide a ment system of reduced developer contamination to the mechanical movements and paper supply.

It is another object of this invention to provide a development system having reduced maintenance.

It is another object of this invention to provide a development system of reduced developer consumption.

It is another object of this invention to provide better removal of developer material from the applicator surface and edges.

It is another object of this invention to provide a simple method of doctoring an applicator surface.

It isanother object of this invention to provide a development system capable of continuous development.

, It is another object of this invention to provide a development system in which the accumulation of excessive developer material at the edge and corner of the applicator surface is prevented.

It is another object of this invention to provide a development system which is superior to known development systems.

The above objects and others are accomplished, generally speaking, by providing edge and corner doctor surfaces at each end of the applicator surface in a position such that when the applicator surface is initially supplied with excessive quantities of developer material and moved against the edge and corner doctor surfaces, the excessive quantities of developer material on the edge and corner of the applicator surface are removed by the scraping action of the edge and comer doctor surfaces. In the continuous or intermittent operation over a period of time the bead of developer material, which normally forms at the edge and comer of the applicator surface, is wiped substantially clean by the edge and comer doctor surfaces. Following this comer doctoring, the partially doctored applicator surface is then doctored with a main or principal doctor surface along a line extending across the entire applicator surface. Developed images and transferred copy prints obtained are generally free of the undesirable background lines or areas along the edges of the image. g

The edge and comer doctoring surfaces may be provided by a blade type device having doctoring surfaces in the configuration of the applicator surfaces. These edge and corner doctoring surfaces may also be provided by a small edge and corner doctoring roll having a pattern cut into the roll to provide the two doctoring surfaces, and the roll being rotatably mounted such that doctoring of the applicator surfaces is achieved. The main doctoring surfaces may also be provided by doctoring rolls or blades. Y

The invention may be further illustrated by reference to the accompanying drawings in which:

FIG. 1 is a schematic view of an embodiment of this invention.

FIG. 2 is a view in perspective showing a portion of an embodiment of this invention.

FIG. 3 is a schematic view of an alternative embodiment of this invention. 2 I

FIGS. 4, 5 and 6 illustrate three configurations for the edge and corner doctoring surfaces of this invention. 7

In FIG. 1, developer feed roll 11, rotatably mounted on its longitudinal axis 12, rotates in developer reservoir 13 supplied with developer 14. Feed roll 11 rotates in developer transfer engagement with applicator roll 15 having a regular patterned surface 16 such that developer is transferred to the applicator surface in a very crude unrestricted manner to a partially metered manner. Generally in either case the developer material is present on the applicator surface in a non-uniform manner and, if used as the applicatorsurface for development, would result in unsatisfactory developed image with considerable background deposits. As the applicator roll rotates about its longitudinal axis on shaft 17 after having developer material transferred to it, corner and edge doctor blade 18 held in place by positioning member 19 scrapes excess quantities of developer material from the edge of the applicator surface and removes developer which has run over onto the corner or vertical edge of the applicator surface. In actual operation, edge and comer doctor blades are provided at each end of the applicator roll. Thereafter, main doctor blade 20 held in place by positioning member 21 removes excess developer from the applicator surface and distributes the developer material uniformly along the surface of the applicator roll. To minimize background deposits the developer material is preferably present in the depressed portions of the applicator surface in developing quantities, while the raised portions are substantially free of developer material. Further rotation of the applicator roll 15 places it in developing engagement with photoconductor surface 22 hearing an electrostatic latent image to be developed. Both corner and edge doctor blades and the principal doctor blade are preferably positioned such that any developer held back by the doctoring surfaces is returned to the developer supply system to minimize contamination of the mechanical movements and paper supply of the developing system.

The configuration and positioning of the edge and corner doctor blade may be more vividly depicted in the perspective view of FIG. 2 wherein developer feed roll 23 is rotatably mounted about shaft 24 which is driven from a source not shown. Feed roll 23 delivers ink from an ink supply to applicator roll 25 rotatably mounted about shaft 26 and driven from an external source. Corner and edge doctor blades 27 are positioned to remove the excessive quantities of developer. material on the edge of the applicator surface, here illustrated as a rotatingarea designated 28, and to remove any accumulated developer material from the corner of the applicator surface here illustrated as rotating area 29. As observed from the drawing, the corner and edge doctor blades are notched such that doctoring in two dimensions is achieved.

In operation, developer would be supplied to the surface of feed roll 23 which, on rotation, would be transferred to applicator roll 25 in unmetered amounts and in undoctored configuration. On rotation, the corners and edges of applicator roll 25 are first scraped free of excess developer by corner and edge doctor blades 27. On further rotation main doctor blade 30, which may extend the entire length of the applicator roll and slightlyover the edge of theapplicator roll, provides the principal doctoring. Further rotation of the doctored applicator surface places the surface in developing configuration with photoconductor surface 31 bearing an electrostatic latent image. I

FIG. 3 is an alternative embodiment of the present invention differing from the embodiment shown in FIG. 1 in the use of a web or belt type applicator surface, in the use of a roller as the main or principal doctoring surface and in the use of a web or belt type photoconductor. More specifically, feed roll 34 feeds developer 32 from developer reservoir 33 to the surface of applicator belt 'or web 38 which is positioned and driven about driving rollers 35. Corner and edge doctor blade 37 held in place by positioning member 36 provides the initial gross doctoring of the edge and corner of the applicator surface. Main doctor roll 39 is positioned and driven to provide doctoring of the entire applicator surface. The doctored applicator surface is then brought into developing configuration with belt or sheet type photoconductor 40 supported by backup roll 41. Doctoring with a doctor roll may be provided according to the technique described by G. Carr in copending application Ser. No. 838,133, filed concurrently and entitled IMAGING SYSTEMS AND METHODS. Therein disclosed is a technique of doctoring applicator surfaces wherein an applicator surface is movedin contact against a moving doctoring'surface such that a differential peripheral speed is obtained between the applicator surface and doctoring surface resulting in 'a net wiping action opposite in direction to the direction of the applicator surface.

While the feed surface has been illustrated as a roll in each of FIGS. 1, 2 and 3, any device suitable for applying developer material to the applicator surface in relatively unmetered fashion may be employed. For example, a web or belt type feed surface maybe used or the developer may be loaded directly onto the applicator surface from a developer reservoir or dispensing member.

FIGS. 4, 5 and 6 illustrate three forms of the comer and edge doctor devicev showing the two doctoring surfaces. In FIG. 4, surface 42 of a blade doctor is positioned to doctor the edge of the applicator surface while surface 43 is positioned to doctor the corner or end face of an applicator surface such as the corner of a roll. In FIG. 5, surface 44 of a blade doctor is the applicator edge doctoring surface, while surface 45 is positioned to doctor the corner of an applicator such as the comer of a web or belt type applicator. In FIG. 6 a rotating doctoring device is depicted wherein the doctoring surfaces are provided by attached cylinders of different diameter such that surface 46 doctors the edge of the applicator while surface 47 doctors the corner of the applicator surface.

The foregoing description of the figures of the drawing describes in general a path of development provided by the applicator surface and along this path inan orderly sequence of steps or stations are provided a developer feed station, a first edge and corner doctoring station, a principal doctoring station, and a development station. This sequence is not intended to be exclusive of all other stations but merely to define the essentials of this invention. A cleaning station could, for example, be provided on the applicator surface. In addition, image transfer and fixing stations may be employed as may also a developer cleaning station when a reusable photoconductor is to be employed.

According to this invention, feeding engagement between the applicator surface and a developer supply may be supplied directly from the reservoir or through some intermediate means such as a feed roller. It is necessary only that image developing quantities of developer be supplied to the applicator surface. This engagement may provide a relatively uncontrolled or unmetered application of developer to the applicator surface in undoctored configuration. The amount of developer transferred to the applicator surface may be controlled by adjusting the clearance between the feed surface and applicator surface. By providing a small clearance between these two surfaces a gross doctoring of the applicator surface may be obtained. The developer loaded applicator surface is then brought into a first doctoring configuration or engagement with the edge and corner doctor to remove excess developer from the edges and to remove excess developer and prevent accumulation of developer on the comers of the applicator. At this first doctoring configuration, the doctoring surfaces and applicator surface are sopositioned as to provide the scraping necessary to this result. Thereafter, the applicator surface is positioned in a second doctoring configuration where the entire dimension of the applicator surface substantially perpendicular to the direction of movement is presented to a doctoring surface in such a manner that excess developer is removed while uniformly supplying developing quantities of developer to the applicator surface. The thusly treated applicator surface in doctored configuration is moved along its path to the developing station and placed in developing engagement with the image to be developed. The positioning is in that manner necessary to accomplish development by electrophoretic development techniques, polar liquid development techniques, selective wetting techniques or dry xerographic development.

The term edge and corner doctoring is intended to define doctoring wherein that portion of the applicator surface adjacent the lateral extremities of the path defining applicator surface is doctored by the edge portion of a doctor surface and that portion of the applicator which may be described as the end face or surface or vertical edge and which is not part of the actual applicator surface is doctored by the corner portion of the doctoring surface. The edge and corner doctoring device, therefore, provides a doctoring in two dimensions, one on the actual applicator surface or edge and the other along the end face of the applicator or corner.

The principal doctoring is accomplished on the entire applicator surface as it moves past the'doctoring surface which dimension on the applicator surface, for the sake of brevity, is hereafter referred to as the width of the applicator surface and is intended to include, for example, the dimension measured on the surface but along the longitudinal axis of an applicator roll or the width of a moving belt. The doctoring surfaces and applicator surface are in developing configuration along a line or small area the width of which is principally determined by the width of the doctor blade or the diameter and hardness of a doctor roll. In all cases, however, the terms doctor line or doctoring path are intended to include both a line and a small area doctoring.

In operation, the corner and edge doctor surfaces provide a gross doctoring of the corner and edge of the developer loaded applicator surface. While the purpose of the main doctor surface is to provide a final metering of developer material to the applicator surface in doctored configuration along the entire developer surface, the corner and edge doctor surfaces provide a rough doctoring of the edge of the applicator surface and prevent the accumulation of developer material along the corner of the applicator surface.

Preferably the comer doctor surface is notched such that the doctoring surfaces conform to the end profile of the applicator surface. For example, when the applicator surface is in the form of a cylindrical roll such that the surface and side form a 90 angle, the doctoring surfaces preferably also are at a 90 angle. By providing doctoring surfaces of substantially the same general configuration as the applicator edge and comer, more efficient removal of excess developer is achieved.

The comer and edge doctor surfaces may be made of any suitable material which is relatively resistant to aging, wearing and chemical attack by the developer. a

The comer and edge doctor surfaces may be made from metals, plastics and elastomeric materials. Typical materials include stainless steel, tempered spring steel, beryllium copper, polyesters such as Mylar, fluorocarbons such as Teflon, Nylon, silicone rubber, fiuorosilicone rubber, urethanes, polyurethanes and polyacrylates.

Since in operation when using a blade doctoring surface there is a pressure buildup on the edge and comer doctor blade due to buildup of developer material being held back by the doctor blade action, the blade should be rigid enough to withstand this pressure.

The corner and edge doctor may be of any suitable size or configuration. When a blade is used it is preferably relatively thin with a smooth doctoring surface since it contacts the applicator surface along a very narrow line or path due to either the circular configuration of a rotating applicator roll or the configuration of a backup rollor other support surface on the underside of a web or belt type applicator. It generally may be from about 0.005 to about 0.090 inches thick. To accomplish the desired result the blade is preferably made of an ap propriate thickness to provide an acceptable rigidity. Preferably to provide the desired rigidity the blade is from about 0.005 to about 0.010 inches thick when made out of metal, from about 0.010 to about 0.045 inches thick when made out of any of the suitable elastic materials and from about 0.045 to about 0.090 inches thick when made out of a suitable elastomeric material. That portion of the blade which doctors the edge of the applicator surface may be of any desired length as long as the objective is obtained. Similarly, that portion of the blade which contacts the corner or side of the applicator surface should be sufficiently long to remove any accumulated developer. When employing a cylindrical roll as the applicator surface, the length of this portion of the blade is limited by the plsition of the shaft about which the roll rotates.'To achieve maximum results, the shape of the doctor blade should conform to the end'profile of the applicator surface.

The edge and corner doctor surfaces may be effectively employed in and out of contact with the surfaces to be doctored. When the doctoring surfaces are not in contact with the surfaces to be doctored, the doctoring action is achieved by virtue of the fact that upon movement of the developer loaded applicator surface past the doctoring surface, only a quantity of developer material which can pass through the spacing between the doctoring surfaces and applicator surfaces remains on the applicator surfaces. Thus, by the selection of small spacings, effective gross doctoring by this technique may be achieved. The spacing selected may be readily determined by one skilled in the art for any given applicator peripheral speed. More effective doctoring, however, is achieved when the edge and corner doctor surfaces and the applicator surface are in contact, since in this configuration more excess developer material is removed. It is preferred to employ a flexible smooth surfaced doctoring surface when the applicator surface and doctoring surface are in contact during doctoring in order to minimize abrasion, distortion of any pattern on the applicator surface and increase the useful life of the applicator surface. v

If more effective doctoring isdesired, the doctoring surfaces may be spring loaded against the applicator surface. It is desirable, particularly when the applicator surface and doctoring surfaces are in contact, that the doctoring surfaces be smooth to minimize any distortion of the applicator surface resulting from continuous contact with a patterned surface.

When the applicator surface is at least a slightly flexible surface as in the case of a web or belt type applicator, the applicator should preferably be securely positioned, and supported at each portion of the development process so thatthe individual operations are accomplished with a minimum of error. For example, a belt type applicator surface should be supported on its underside when in doctoring configuration with a doctor blade or when in feeding or developing configuration. The desirability of such support has been illustrated in FIG. 3 of the drawing. Small rotating rollers that may or may not be independently driven are particularly satisfactory support members.

The edge and comer doctor blade may be positioned against the applicator surface at any suitable angle at which the desired doctoring is achieved. Generally, the blade is positioned within about 45 of either side of the perpendicular to the tangent plane at the point of contact between the blade and applicator surface. An angle of about to the tangent at the point of contact is preferred as producing particularly satisfactory doctoring results. To prevent accumulation of developer on the applicator surfaces after doctoring by the edge and comer doctoring surfaces it is generally preferred to position the comer and edge doctors at a point on the applicator surface where a minimum amount of excess developer previously removed by the doctoring action of the corner and edge doctors may subsequently contact the applicator surface during the same cycle. When an applicator roll is employed as the feed surface the comer and edge doctors may suitably be positioned against the lower half of the applicator roll to achieve this result.

While a blade configuration is preferred for the corner and edge doctor surface since its use requires only a positioning member and no additional driving means, a roller configuration as the edge and corner doctor may be employed. This type of roll would take the appearance of one relatively large roll immediately adjacent to one relatively smaller roll, the smaller roll providing the edge doctoring surface while the larger roll provides the corner doctoring surface. The other limitations placed on blade doctoring surfaces are equally applicable to roll doctoring surfaces. Suitable doctoring may be achieved with this configuration with a stationary or driven roller.

As the applicator surface loaded with unmetered quantities of developer material is moved fromthe developer transfer position to the developing engagement position, the applicator surface is first doctored by the edge and corner doctor device described herein to remove excess developer from the edge portion of the surface of the applicator and to remove any accumulated developer from the corner portion of the applica tor. The applicator surface is then doctore d with the main doctor device removing excess developer from the applicator surface, forming a small pool or ripple of developer between the applicator surface and doctor device, and distributing developer over the length of the applicator surface. Preferably the doctoring is performed so that developing quantities of developer material are present on the applicator surface. When the polar liquid development technique is employed, developing quantities of developer material are preferably supplied to the depressed portions or valleys of the applicator while the raised portions are substantially free of developer thereby reducing background deposits.

It is preferred to position the edgeand corner doctor surfaces ahead of the main doctor surface in order to present a uniformly doctored applicator surface to the image bearing surface. Since the main doctor surface doctors the entire surface of the applicator, and the corner and edge doctors only provide doctoring on the edge portions of the applicator surface, a uniform doctored applicator can best be achieved by positioning the main doctor surface in doctoring configuration after the edge and corner doctor surfaces.

The main doctor device may be made out of suitable material. It may, for example, be made of the same materials discussed with respect to the edge and corner doctor device and may be of any suitable thickness. Depending on the rigidity of the particular material employed, a main doctor blade may typically be from about 0.005 to about 0.1 inches thick, with thinner blades being employed with more rigid materials and thicker blades being employed with less rigid materials. For example, a thickness of from about 0.005 to about 0.010 inches is sufficient for steel while about 0.010 to 0.030 inches is necessary for plastics, and most elastomers require a thickness of from about 0.060 to about 0.090 inches. The main doctor blade preferably has a smooth surface to minimize abrasion of the applicator surface and in addition to doctoring the entire developing surface, it may extend over the edge of the applicator surface to insure uniform doctoring and removal of excess developer.- However, with unsupported blades made of less rigid materials, the extension over the edge of the applicator surface should be relatively small since with too long an extension the blade may tend to ripple or wave along the ends of the applicator surface.

To obtain adequate doctoring the main doctor blade is preferably in contact with the applicator surface under pressure, which pressure is controlled by manual adjustment of set screws in the doctor blade assembly. With increasing pressure, more developer is removed from the applicator surface so the selection of appropriate pressure may be obtained by a simple observation of the quality of print obtained and the pressure regulated accordingly. If too much pressure is applied, the print will be ill defined lacking in density and contrast whereas with too little pressure large background deposits may be observed. v

The main doctor blademay be positioned at any suitable exterior angle to the applicator surface. If the angle formed between the doctor blade and the tangent plane at the line of contact ofthe applicator surface and the doctor blade is a very small acute angle, less doctoring is achieved. Typically an angle of from about 45 to about75 between the doctor blade and the tangent plane at thev line of contact with approaching applicator surface is employed. Particularly preferred doctoring results being obtained at an angle of about 60 with a metal or plastic doctor blade and at an angle of about 45 with elastomeric doctor blades. It is also possible to use reverse angle doctoring wherein the main doctor is positioned so that an obtuse angle is formed between the blade and the tangent to the applicator surface approaching the doctor blade at the line of contact.

Any suitable developer applicator, surface may be employed. Typical developer applicator surfaces include rotatably mounted rollers or movable endless webs or belts having a smooth surface or uniform pattern surfaces of raised portions or lands and depressed portions or valleys. A desirable applicator is a cylindrical roll having a trihelicoid, pyramidal or quadragravure pattern on the surface. Particularly satisfactory print quality and operating performance is obtained with a roll having a trihelicoid pattern of between 80 and 300 lines per inch, with about 180 to 250 being preferred, cut at an angle of from about to about 60, referably from about 30 to 60 to thelongitudinal axis and to a depth of from about one and one-half mils to about 6 mils. Optimum print capability is obtained with grooves cut at an angle of about 45 to the longitudinal axis.

Any suitable developer may be employed. Typical developersinclude polar and non-polar liquids and dry powdered electroscopic materials. It is desirable that the developers be compatible with the particular materials they come in contact with during the development. The liquid developer may have any suitable pigment dispersed or dye dissolved therein. Typical liquid developers useful may be selected from the commercially available water, oil and alcohol based inks and include among others as vehicles mineral oil, castor oil, peanut oil, coconut oil, corn oil, rape seed oil, sunflower seed oil, oleic acid, polypropylene glycol, mineral spirits, glycerol and sorbitol. Suitable colorants include carbon black and other particulate forms of carbon, iron oxide, zinc oxide, titanium dioxide, I ultrarnarine blue, methylene I blue, methyl violet tannate. Dispeisants, humidity control and DESCRIPTION OF PREFERRED EMBODIMENTS The following preferred nonlimiting example further defines, describes and exemplifies the technique of the present invention. Example II is presented for comparative purposes. In the examples all parts and percentages are by weights unless otherwise specified.

EXAMPLE I A rotatably mounted machine surfaced steel cylindrical roll is positioned as a developer feed such that the lower portion thereof is in a developer bath containing liquid developer of the following composition by weight:

Light Mineral Oil 45 parts by weight Microlith CT 27 parts by weight Ganex V216 23 parts by weight VM550 Methyl 4 parts by weight Paraflint RG Wax 1 parts by weight Microlith CT is a resinated predispersed carbon black pigment composed of about 40 percent carbon black and 60 percent ester-gum resin and manufactured by CIBA. Ganex V216 is an alkylated polyvinyl pyrrolidone dispersant manufactured by GAF Corp. VM550 is a flushed pigment in mineral oil manufactured by Magruder Color Co. Paraflint is a hard synthetic wax manufactured by Moore and Munger Co.

The feed roll as it rotates in the bath picks up developer and on further rotation delivers this developer to a rotatably mounted cylindrical applicator roll having a trihelicoid surface pattern of about 180 threads per inch cut at an angle of about 45 to the axisand to adepth of about 0.002 inches. After this transfer the developer'is uniformly presented on the applicator roll in excessive quantities. As the applicator roll rotates about its axis at a circumferential speed of about 12 inches per second, edge and comer doctor blade at each end of the applicator roll made of a phenolic resin bound paper laminate and about 0.030 inches thick and positioned at an angle of about to the tangent at the line of contact between the applicator roll and blade removes excess developer from both edge and both corners of the applicator roll. As the applicator roll further rotates a principal stainless steel doctor blade about 0.008 inches thick and positioned at an angle of about 60 to the tangent at the line of contact between the applicator roll and blade and extending the entire length of the applicator roll provides the final doctoring of the applicator roll. Developing quantities of developer are present in the grooves of the applicator surface while the raised portions are substantially free of developer. The applicator roll further rotates to contact the image bearing surface which in this example is a paper backed zinc oxide binder layer which has previously been charged and exposed in conventional manner. The applicator roll is rotatably advanced over the zinc oxide paper to develop the image. The developer on the zinc oxide paper is transferred to Xerox 4024 Paper in image configuration. The print was of acceptable quality.

EXAMPLE Il The procedure of Example I is repeated with the exception that the edge and comer doctor blades are removed. All prints were of unacceptable quality since very noticeable streaks of background are obtained on both edges of the copy paper.

Although specific materials and techniques are set forth in the exemplary embodiments using the doctoring technique of this invention, these are merely intended as illustrations of the present invention. There are other materials and techniques and modifications of the present invention which will occur to those skilled in the art upon reading of the present disclosure which materials, techniques and modifications are intended to be included within the scope of this invention.

What is claimed is:

1. A development system comprising means to feed developer to an applicator surface, comer and edge doctoring means to provide a gross doctoring of the comers and edges of the applicator surface, principal doctoring means to provide a uniform doctoring along a line extending across the entire applicator surface, an imaging surface bearing an image'to be developed, means to sequentially drive the applicator surface through the developer feed means, the corner and edge doctoring means, the principal doctoring means and position the applicator surface in developing configuration with the image bearing surface.

2. A development system comprising,

a developer reservoir containing developer in feeding engagement with a rotatably mounted developer feed roller means;

a rotatably mounted applicator roll means in developer transfer engagement with said feed roll means;

1. corner and edge doctoring means having corner and edge doctoring surfaces in doctoring engagement with the corners and edges of said applicator roll means; principal doctoring means having a principal doctoring surface in doctoring engagement with said applicator roll means to provide uniform doctoring along a line extending across the entire applicator surface; and

an image bearing surface in developing relationship with said applicator roll means.

3. A development system comprising a path defining movable developer applicator surface and sequentially positioned along the applicator surface path a developer feed means, an edge and corner applicator surface doctoring means, principal applicator surface doctoring means, an imaging surface in developing engagement with the applicator surface and means to move the applicator surface along the means defining path.

4. The system of claim 3 wherein the path defining movable developer applicator surface is a cylindrical roll, edge and comer doctoring means is provided by blades having doctoring surfaces which conform to the end profiles of the applicator roll and the principal doctoring surface means is a blade doctor.

5. The system of claim 4 wherein the applicator roll has a regular surface pattern of raised and depressed positions. 

1. A development system comprising means to feed develoPer to an applicator surface, corner and edge doctoring means to provide a gross doctoring of the corners and edges of the applicator surface, principal doctoring means to provide a uniform doctoring along a line extending across the entire applicator surface, an imaging surface bearing an image to be developed, means to sequentially drive the applicator surface through the developer feed means, the corner and edge doctoring means, the principal doctoring means and position the applicator surface in developing configuration with the image bearing surface.
 2. A development system comprising, a developer reservoir containing developer in feeding engagement with a rotatably mounted developer feed roller means; a rotatably mounted applicator roll means in developer transfer engagement with said feed roll means; corner and edge doctoring means having corner and edge doctoring surfaces in doctoring engagement with the corners and edges of said applicator roll means; principal doctoring means having a principal doctoring surface in doctoring engagement with said applicator roll means to provide uniform doctoring along a line extending across the entire applicator surface; and an image bearing surface in developing relationship with said applicator roll means.
 3. A development system comprising a path defining movable developer applicator surface and sequentially positioned along the applicator surface path a developer feed means, an edge and corner applicator surface doctoring means, principal applicator surface doctoring means, an imaging surface in developing engagement with the applicator surface and means to move the applicator surface along the means defining path.
 4. The system of claim 3 wherein the path defining movable developer applicator surface is a cylindrical roll, edge and corner doctoring means is provided by blades having doctoring surfaces which conform to the end profiles of the applicator roll and the principal doctoring surface means is a blade doctor.
 5. The system of claim 4 wherein the applicator roll has a regular surface pattern of raised and depressed positions. 